1. Field of the Invention
The present invention relates to a semiconductor device and a package for a semiconductor device, and more particularly, it relates to an improvement of a semiconductor device for protecting a semiconductor chip against light.
2. Description of the Background Art
In recent years, a semiconductor chip is generally directly housed with a molded resin material, to be applied to a semiconductor device. The semiconductor chip is mainly covered with an epoxy resin material, which is mixed with a coloring agent such as carbon black, a filler and the like at need. In a conventional semiconductor device, such a resin material protects the semiconductor chip against light.
In relation to semiconductor devices having photodetectors, there have been reported various light shielding means, which are adapted to prevent portions other than such photodetectors from irradiation of light. For example, Japanese Patent Laying-Open No. 62-205649 (1987) discloses a semiconductor device comprising a photodetector and an IC connected thereto, which are sealed with a light transmitting resin material. The resin material is covered with a light shielding coating material, except for a window for applying light to the photodetector. Japanese Patent Laying-Open No. 1-147853 (1989) discloses a photodetector module comprising an IC having a photodetector such as a photodiode and an amplifier circuit provided on the same substrate and a photoresist material covering the same, which are housed in a clear mold package. In such a module, a frame covers the IC so that no light is applied to portions other than the photodetector, while the same is provided with a window for applying light to the photodetector. Japanese Patent Laying-Open No. 1-152664 (1989) discloses a semiconductor device comprising an integrated circuit pellet containing a photodetector which is housed in a light transmitting resin package. In such a semiconductor device, a plate having a through hole in a position corresponding to the photodetector is brought into close contact with the surface of the resin package. This plate is prepared from aluminum, for example, to intercept light. Thus, it is possible to apply light only to the photodetector through this plate.
With recent prevalence of note-type personal computers and electronic notebooks, ICs are increasingly reduced in size and thickness. Further, packages for dynamic RAMs, One Time Programmable ROMs and the like are also increasingly reduced in thickness and weight. Consequently, TSOPs (thin small outline packages), which are only about 1 mm in thickness, are put into practice in succession.
However, while a conventional resin package for a semiconductor device has a sufficient thickness for intercepting light, the thickness of a resin material forming a TSOP is so small that light may reach a semiconductor chip. If light passes through the resin material to reach the semiconductor chip, the storage contents of a memory may be erroneously erased in the case of the One Time Programmable ROM, while a malfunction may be caused by leakage of a cell charge or a leakage current in a circuit part in the case of a dynamic RAM. The degree of such a malfunction may depend on intensity of the light and the thickness of the resin material.
The aforementioned techniques regarding photodetectors can be applied in order to solve such a problem. However, none of such techniques can guarantee a sufficient light shielding property while maintaining the package in the reduced thickness and weight.